In Roman times, the Nederrijn flowed into the Kromme Rijn and these streams were the main outflow of the river Rhine.

A short distance past Wijk bij Duurstede, the river intersects with the Amsterdam-Rhine Canal, which continues south towards the Waal.

Other major towns on its banks are Culemborg, Vianen, Schoonhoven, Nieuw-Lekkerland, Lekkerkerk, Bergambacht, and Krimpen aan de Lek.

The bed of the river lies slightly higher than the surrounding lands and dikes are therefore essential to contain the Lek.

At the village of Kinderdijk the Lek meets the Noord River and the combined stream is thereafter known as the Nieuwe Maas as it flows down towards the North Sea.